Brian Williams Stalks Jon Hamm on 'Late Night' (VIDEO)

Jon Hamm's favorite sketch from his two times as host of 'Saturday Night Live' involved Will Forte, when Forte was a Halloween trick-or-treater costumed as a child molester. "It was hilariously awkward, and Will does that very well," Hamm told former 'SNL' cast member Jimmy Fallon on 'Late Night' (weeknights, 12:37AM ET on NBC).

But that skit was originally meant for 'NBC Nightly News' Anchor Brian Williams. The newsman saw its rehearsal on the intra-network NBC feed and sent a personal message to them saying, "Why is there some idiot in a Charlie Brown sweater doing my sketch? Lose my number! Love, Brian Williams."

Maybe Williams was just jealous that he didn't get to spend time with Hamm while he was in proximity. He loves the actor and 'Mad Men.' Fallon warned, "You gotta watch it when you're in this building ... He watches the feed. He could show up wherever." At that moment, the cameras panned to the studio door, with a fanatic Williams peering through the window. Hamm's reaction? "That's just sad."